The present invention relates to a flow check valve for fluid systems and more particularly to a spring-biased, normally open check valve which passes fluid flow in a forward direction and prevents passage of flow in a reverse direction. The valve has the unique capability for bias spring removal and replacement while on-line and in-service without affecting the pressure boundary integrity of the downstream portion of the system so long as that portion of the system is under pressure.
In certain fluid systems, either gas or liquid, it is sometimes necessary, or at least desirable, to employ a reverse flow blocking device, or check valve, downstream of certain system components such as pumps as a safety feature so as to prevent backflow of fluid through them which could have deleterious effects. For example, in a crane or jack which is actuated by means of a hydraulic cylinder, should a hose leading to the cylinder develop a leak or should the pump fail, the hydraulic fluid will tend to leave the cylinder rapidly and the crane or jack will no longer support a weight carried thereby. However, if a spring-biased flow check valve is provided in the fluid supply line adjacent to the hydraulic cylinder, the normal resistance of the bias spring present in the valve will be overcome by the flow of the fluid from the cylinder and a valve member within the flow check valve will shut off the fluid flow until necessary repairs can be made.
However, in spring-biased check valves the bias spring may take a set, thus it is desirable to replace the biasing spring from time to time, especially in systems where it is desired to have a check valve that closes at a certain predetermined back pressure. Thus, it is desirable to have a flow check valve wherein in-service replacement of the bias spring can be performed while the valve remains on-line. Also, in some instances it is desirable to have bias spring replacement capability while system pressure is maintained in that portion of the system which is downstream from the flow check valve.
Also, in some systems reaction products, sludge products, corrosion products, erosion products, or the like may form and circulate within the system. The existence of such products may depend, in part, upon the fluid, system component materials, flow velocities, temperature, pressure, or upon other physical, chemical, and thermodynamic properties. These products tend to be created at and/or lodge in areas of the system which are subject to step changes, or large gradients, in temperature, pressure, and velocity, or in areas at material interfaces. Most often, the products accumulate in areas of reduced diameter or around projections into the flow stream. Thus, the products can accumulate on the portions of valves which project into the flow stream. Consequently, valves, and particularly check valves, which may have plug members, cage guides, seat rings, shaft members, and other valve trim which project into the flow stream or which are of materials different from other parts of the valve or piping system, can become a trap for flowing crud products, if not actual producing points of such products.
U.S. Pat. No. 2,375,498 to Seymour discloses a fluid lockout device which utilizes a resilient, yieldable valve member capable of permanently sealing a hydraulic conduit within which a substantial portion of the valve member is received. However, the bias spring present in the device of Seymour cannot be removed or replaced without complete disassembly of the device and attendant release of the downstream pressure.